High storage-DVDs created using gold-nanorods

Researchers at the Swinburne University of Technology, in Hawthorn, Australia, have found a way to add two more dimensions to optical-disc recording: wavelength and polarization. The technique could pack 1.6 terabytes of data on a standard-size DVD, —the equivalent of 30 Blu-ray discs. Moreover, it could be compatible with today’s disk-drive technology.
The Australian researchers are very optimistic about this new technology. They say that data recording could be done with a cheaper laser diode and that high-speed recording and readout should be possible. They have signed a research agreement with Samsung and believe that the technology will be available commercially in 5 to 10 years.

Their research involves making a new kind of disc. They dispersed gold nanorods of three different sizes in a polymer solution, coated thin glass films with the solution, and then used glue to assemble a stack of three of the films, one on top of the other.

For recording the disc, a tunable laser is focussed on 750-nanometer-wide spots on a gold nanorod layer. The tiny rods have a tendency to collapse into spheres when they absorb light and are heated to a certain threshold. But the rods are selective. Nanorods of a specific size absorb a specific wavelength and then only if they are aligned with the direction of the light’s polarization. Under those conditions, the energy waves traveling along the rods’ surface—called surface plasmons—resonate with the light’s frequency. So when the laser beam is focused on the bits, only some of the rods turn into spheres.

There are many different sizes of rods in random orientation.Light impinging with a certain color and polarization will only target a subpopulation of gold nanorods, leaving the remaining rods for the next recording. That means each bit area can hold multiple bits. To demonstrate the technology, reserachers created six patterns on each of the three nanorod layers by focusing light on a grid of 75-by-75 bits. The volume of their disk is about 12 cm³, which gives a total data capacity of 1.6 terabytes.

Reading the bits involves focusing light from the same laser on the bits but with much lower energy. The nanorods shine when they absorb the dim light, which must be of the same wavelength and polarization that could change their shape during recording.

People have been thinking about 3-D optical data storage for a while, but this is the first time data has been recorded and read in five dimensions

Identification of Additional Plasmon Mode for Triangular Gold Nanoprism

The use of anisotropic nanomaterials in applications such as biodetection,catalysis,and electronics has led to a continuously increasing interest in the development of synthetic methods for preparing new shapes.
In particular,triangular nanoprisms are a class of nanostructures that have generated intense interest due to their unusual optical properties and the recent development of new methodologies for preparing bulk quantities of them. Gold nanoprisms have been synthesized exclusively by thermal methods with varying degrees of success regarding purity and size control.The optical spectra of nanoprisms should exhibit a distinct dipole resonance as observed in isotropic spherical structures in addition to weaker higher order resonances.The identification of higher order surface plasmon resonance modes with these nanostructures is important because it provides not only greater understanding of their physical properties but also a spectroscopic fingerprint that can be used to characterize and assess the quality of such structures. Recently researchers presented a synthetic approach and separation procedure for synthesizing and isolating large quantities of gold nanoprisms with uniform edge lengths and thicknesses, which has allowed the use of UV−vis−NIR spectroscopy to observe an in-plane quadrupole resonance mode of such structures.
The researchers have develop a method for synthesizing Au nanoprisms in their purest form. The purity of such materials has allowed them to correlate their structure with their optical properties and identify the quadrupole plasmon resonance, which has never been observed in solution because of inhomogeneity and impurities found in the products formed from other preparatory procedures. In view of the high stability of gold as compared with silver, these structures should provide a route to synthesizing many technologically useful materials not attainable with their less noble analogue.

Gold Nanorods Assemblies with Nano Gaps

Gold nanorods continue to gather increasing interest due to their facile synthesis, unique optical properties, and potential for medical and electronic applications. To take advantage of these properties, several research groups are pursuing methods to self-assemble or to arrange these nanomaterials into useful formations.End-to-end assemblies are of particular appeal since gaps between the nanorods could serve as spacers for single-molecule electronic devices. Several successful approaches to accomplish end-to-end assembly have been reported in the literature; however, each of these approaches relies on modifying already synthesized gold nanorods by adding the desired linker agent.

Seeking a new bottom-up technique to generate gold nanorods assembled end-to-end, researchers have developed a novel method to grow the rods directly from chemically linked seed particles. The researchers started with citrate-stabilized gold nanoparticles, then allowed these seeds to self-assemble using a water-soluble dithiol-functionalized polyethylene glycol linker. The seed particle dimers were then exposed to growth conditions similar to those typically used to form unlinked gold nanorods, extending each rod to a length of 500 nm. About 55% of the rods grown using this method were linked end-to-end. Transmission electron microscopy revealed a gap of 1−2 nm between these linked rods, a size well-suited for placing a single molecule within the gap. The linked nanorods were flexible around the hinging molecule, demonstrated by flow linear dichroism. The researchers suggest that exposing the linked nanorods to a low-concentration solution of an electronically relevant molecule would result in one or a few molecules within each nanogap, enabling single-molecule electronic measurements.